GB1572021A - Process for the production of hexachlorocyclobutene - Google Patents

Description

PATENT SPECIFICATION

( 11) 1 572 021 ( 21) Application No 17511/77 ( 22) Filed 27 Apr 1977 ( 19) ( 31) Convention Application No 2618557 ( 32) Filed 28 Apr 1976 in ( 33) Fed Rep of Germany (DE), ( 44) Complete Specification Published 23 Jul 1980 ( 51) INT CL 3 C 07 C 23/06 ( 52) Index at Acceptance C 2 C 1174 200 227 22 X 22 Y 305 313 31 Y 338 565 69 Y FH HG ( 54) A PROCESS FOR THE PRODUCTION OF HEXACHLOROCYCLOBUTENE (.71) We, CHEMISCHE WERKE HULS AKTIENGESELLSCHAFT a Germany Company of 4370 Marl Federal Republic of Germany do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the follow-

ing Statement:-

The invention relates to a process for the production of hexachlorocyclobutene from commercial hexachlorobutadiene.

Hexachlorocvclobutene is an interesting intermediate for the synthesis of organic compounds It is obtained in the laboratory bv the reaction of hexafluorocyclobutene with aluminium chloride It is possible to enrich hexachlorocyclobutene up to about % from commercial hexachlorobutadiene by vacuum fractionation and low temperature crvstallisation (Angew Chem 78 ( 1966) page 928 last paragraph to page 929, third paragraph) It is moreover known that hexafluorobutadiene and hexachlorobutadiene can be rearranged in an equilibrium reaction into hexafluorocyclobutene and hexachlorocyclobutene respectively In the case of the hexafluoro derivative the cyclic structure is the more stable thermodynamically but in the case of hexachlorobutadiene the open-chain structure is strongly favoured (Angew Chem 78 ( 1966) page 928, last paragraph to page 929 second paragraph) According to the said publication cvclisation of hexachlorobutadiene into hexachloroevclobutene is just as unsuitable as a distillative purification because a 20 % enrichment is completely inadequate industriallv.

The problem therefore remains of producing hexachlorocyclobutene in high purity in an economical manner from raw materials which are easily accessible commerciallv.

According to the present invention there is provided a process for the production of hexachlorocyclobutene wherein commercial hexachlorobutadiene containing hexachlorocyclobutene is rectified in a column at a pressure of from 2 to 100 mm Hg with a reflux ratio of from 300 to 600, a fraction rich in hexachlorocyclobutene is withdrawn over the top from the column as overhead fraction and is if necessary or desired fractionally crystallised, and hexachlorobutadiene remaining in the bottoms fraction is subjected to a heat treatment at from 150 to C and these returned in addition to fresh commercial hexachlorobutadiene to the rectifying column.

Hexachlorobutadiene containing hexachlorocyclobutene occurs as an undesired byproduct in the production of perchlorinated hydrocarbons By a heat treatment at 150 to 200 C preferably from 180 to 200 C a part of the hexachlorobutadiene is cyclised into hexachlorocyclobutene, cyclisation to the extent of 1 0 to 1 9 % occurring with a residence time of from 2 to 120 minutes, preferably from 3 to 10 minutes Practically the whole of the hexachlorobutadiene can be rearranged into hexachlorocyclobutene by rectifying separation of the hexachlorocyclobutene formed and repeated heat treatment of hexachlorobutadiene.

Rectification is carried out in a column advantageously one having from 50 to 150, preferably from 70 to 100, theoretical trays.

Columns packed with wire mesh rings or wire gauze or in general, columns having a small pressure drop per theoretical separation stage may be used with advantage.

Rectification is carried out at a pressure of from 2 to 100, preferably from 15 to 50 mm Hg and at a reflux ratio of from 300 to 600 and preferably from 350 to 500 Suitably the bottoms temperature is from 100 to 140 C and preferably it is from 110 to C The temperature in the enrichment section of the rectifying column, which cq tn 1 572 021 generally corresponds to the region from the 1st to 100th theoretical trays and preferably from the 10th to the 100th theoretical trays, is preferably below 120 C In the production of highly enriched hexachlorocyclobutene it is moreover advantageous, when using a rectifying pressure of from 3 to 30 mm Hg.

to keep the temperature of the cooling medium in the condenser associated with the column above the melting point of hexachlorocyclobutene, for example at 51 C.

Practically pure hexachlorocyclobutene crvstallises out from mixtures of hexachlorocyclobutene and hexachlorobutadiene in which the hexachlorocyclobutene is highly enriched: this crystallization already occurring at about 44 C from 80 % pure hexachlorocyclobutene Rectification therefore need not be carried bevond a concentration of 80 % and the hexachlorocyclobutene can then be further purified by a fractional crystallisation.

Continuous recovery of hexachlorocyclobutene is particularly advantageous In one example of such a process a product freed from other substances by rectification and consisting mainly of hexachlorobutadiene with small amounts of hexachllorocvclobutene is rectified in the said manner so that a highly enriched hexachlorocvclobutene is obtained as the overhead fraction and there is continuously withdrawn from the bottoms of the rectification column a bottoms fraction which is then heated to a temperature of for example 200 C and returned to the rectification column This return mav be to the bottoms or more conveniently, at the level at which the raw material is fed in.

From such an apparatus practically the whole of the hexachlorobutadiene supplied, as well as anv small amounts of hexachlorocvclobutene supplied, can be withdrawn over the top of the column as a high percentage hexachlorocyclobutene.

The following Example illustrates the invention.

Example

Into an experimental apparatus as shown in the accompanving diagrammatic drawing, commercial (crude) hexachlorobutadiene.

such as is obtained for example in a plant for the production of carbon tetrachloride and perchloroethvlene by chlorination of mixtures of various chlorohvdrocarbons such as chloroform dichloroethane and others, and which has been previously distilled to separate other constituents is fed through line 1 to the rectifying column 2 The column used is 10 metres in height (a so-called Sulzer column), has about seventy theoretical trays and is packed with wire gauze Supply takes place about 1 metre above the bottom of the column The overhead vapour from the column is completely condensed in a condenser 8 and some of the condensate is withdrawn as product through line 3 while the reflux returns to the column through line 4 A stream is withdrawn from the bottom of the column through line 5 and, by means of a pump 6, is passed through a heater 7 and then back into the rectifying column.

The pressure at the top of the column is kept at 25 mm Hg so that, at a reflux ratio of 450.

a temperature of 101 C is set up at the top of the column The overhead product contains 98.6 % by weight of hexachlorocyclobutene (remainder hexachlorobutadiene) and has a melting point of about 50 O C The withdrawn bottoms fraction has a concentration of 1 1 % by weight of hexachlorocyclobutene whereas the stream leaving the heater 7 has a concentration of 1 8 % by weight of hexachlorocyclobutene The feed also has this concentration At a differential pressure of the column of 21 mm Hg the temperature at the bottom of the column is C The bottoms fraction withdrawn through line 5 is heated to 200 C in the heater 7 with a mean residence time of about ten minutes.

Claims (9)

WHAT WE CLAIM IS:-

1 A process for the production of hexachlorocyclobutene wherein commercial hexachlorobutadiene is rectified in a column at a pressure of from 2 to 100 mm Hg with a reflux ratio of from 300 to 600, a fraction rich in hexachlorocvclobutene is withdrawn from the column as the overhead fraction, and hexachlorobutadiene remaining in the bottoms fraction is subjected to a heat treatment at from 1500 C to 200 C and then returned to the rectifying column in addition to fresh commercial hexachlorobutadiene.

2 A process as claimed in claim 1 wherein the overhead fraction rich in hexachlorocyclobutene is subjected to fractional crvstallisation.

3 A process as claimed in claim 1 or 2 wherein the enrichment section of the rectifying column is kept at a temperature below 120 C.

4, A process as claimed in any of claims 1 to 3 wherein the rectification is carried out in a column having from 50 to 150 theoretical trays.

A process as claimed in any of claims 1 to 3 wherein the rectification is carried out in a column having 70 to 100 theoretical travs.

6 A process as claimed in anv of claims I to 5 wherein the rectification is carried out at a reflux ratio of 350 to 500.

7 A process as claimed in anv of claims 1 to 6 wherein the rectification is carried out at a pressure of 15 to 50 mm Hg.

8 A process as claimed in any of claims 1 to 7 wherein the heat treatment is carried out at 180 to 200 C for from 2 to 120 3 1 572 021 3 minutes.

9 A process for the production of hexachlorocyclobutene as claimed in claim 1 carried out substantially as hereinbefore described or illustrated with reference to the accompanying drawing or in the foregoing Example.

Hexachlorocvclobutene when produced by a process as claimed in any of claims 1 to 9.

J Y & G W JOHNSON, Furnival House, 14-18 High Holborn, London WC 1 V 6 DE.

Chartered Patent Agents, Agents for the Applicants.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1980.

Published by The Patent Office, 25 Southampton Buildings, London WC 2 A IAY, from which copies may be obtained.